Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

Example embodiments relate to methods of controlling hydrogen
concentrations in an offgas system of a nuclear reactor by passive air
injection. A method according to a non-limiting embodiment may include
passively injecting ambient air through the hydrogen water chemistry
system into an existing offgas line of the offgas system. The offgas line
is configured to transport non-condensable gases, including hydrogen,
from a condenser to a recombiner. As a result of the passive air
injection, the combined flow of hydrogen and oxygen react in the
recombiner to form water vapor, thereby reducing the hydrogen
concentration of the offgas exiting the recombiner.

Claims:

1. A method of controlling hydrogen concentrations in an offgas system of
a nuclear reactor by hydrogen water chemistry system injection, the
method comprising: passively injecting ambient air through the hydrogen
water chemistry system into an existing offgas line of the offgas system,
the offgas line configured to transport gases containing hydrogen,
oxygen, and other non-condensable gases from a condenser to a recombiner,
the recombiner configured to react hydrogen with oxygen to form water
vapor.

2. The method of claim 1, wherein the ambient air is passively injected
into the offgas line at a point upstream from the recombiner.

3. The method of claim 1, wherein the ambient air is passively injected
by opening an automatic valve and having the ambient air drawn into the
offgas line by a vacuum exerted by the offgas system.

4. The method of claim 3, wherein the automatic valve is an air-operated
isolation valve that is controlled through a solenoid valve.

5. The method of claim 3, wherein the automatic valve is a solenoid
valve.

6. The method of claim 1, wherein the ambient air is passively injected
at a desired flow into the offgas line with a critical flow orifice.

7. The method of claim 1, wherein the ambient air is passively injected
at a desired flow into the offgas line with a flow meter and flow control
valve.

8. The method of claim 1, further comprising: filtering the ambient air
prior to injection into the offgas line.

9. The method of claim 1, wherein the ambient air is passively injected
as a backup source of oxygen for the hydrogen water chemistry system.

10. The method of claim 1, wherein the ambient air is passively injected
as a primary source of oxygen for the hydrogen water chemistry system.

11. A method of passively injecting air through a hydrogen water
chemistry system into an offgas system of a nuclear reactor, the method
comprising: operatively coupling an air injection line to an existing
offgas line of the offgas system, the offgas line configured to transport
offgas containing hydrogen, oxygen, and other non-condensable gases from
a condenser to a recombiner, the air injection line configured to
passively introduce ambient air into the offgas line at a point upstream
from the recombiner to produce a combined flow; measuring a concentration
of at least one of hydrogen and oxygen in an offgas flow exiting the
recombiner; generating an injection signal, the injection signal being
generated as long as the measured oxygen concentration is lower than a
predetermined oxygen value or the measured hydrogen concentration exceeds
a predetermined hydrogen value when the ambient air is being passively
introduced as a backup source of oxygen, the injection signal being
generated as long as the hydrogen water chemistry system is initiated
when the ambient air is being passively introduced as a primary source of
oxygen; and automatically opening a valve in response to the injection
signal so as to passively introduce ambient air as a source of oxygen
into the offgas line, the ambient air being drawn into the offgas line by
a vacuum exerted by the offgas system, the oxygen and hydrogen in the
combined flow reacting in the recombiner to form water vapor.

12. The method of claim 11, wherein the ambient air contains about 21%
oxygen gas.

13. The method of claim 11, further comprising: filtering the ambient air
prior to introduction into the offgas line.

14. The method of claim 11, further comprising: generating a stop signal
as long as the measured oxygen concentration exceeds the predetermined
oxygen value when the ambient air is being passively introduced as a
backup source of oxygen.

15. The method of claim 14, further comprising: automatically closing the
valve in response to the stop signal.

16. The method of claim 11, wherein the valve is an automatic isolation
valve.

17. The method of claim 16, wherein the automatic isolation valve is an
air-operated valve controlled through a solenoid valve.

18. The method of claim 16, wherein the automatic isolation valve is a
solenoid valve.

19. The method of claim 11, further comprising: passively introducing the
ambient air into the offgas line at a desired flow with a critical flow
orifice.

20. The method of claim 19, wherein the critical flow orifice is sized
based on ambient air and offgas pressures.

Description:

FIELD

[0001] Example embodiments of the present invention relate to methods of
controlling hydrogen concentrations in an offgas system of a nuclear
reactor.

DESCRIPTION OF RELATED ART

[0002] A nuclear reactor (e.g., boiling water reactor (BWR)) typically
experiences corrosion caused by oxygen generated from the radiolysis of
water. For instance, the recirculation piping and reactor internals may
experience intergranular stress corrosion cracking (IGSCC). As a result,
a hydrogen water chemistry (HWC) system injects hydrogen into the
condensate/feedwater system to reduce the amount of dissolved oxygen
within the recirculation piping and the reactor internals.

[0003] However, hydrogen injection into the condensate/feedwater may
result in an increase in the normal hydrogen to oxygen ratio of 2:1 in
the offgas. Depending on the amount of hydrogen added and the condenser
air inleakage rate, this increase could result in the offgas at the
recombiner exit becoming hydrogen rich. To prevent this potentially
hazardous situation, additional oxygen is injected into the offgas
system. Conventionally, the additional oxygen is supplied by flowing
compressed air or pure compressed oxygen from a pertinent source. The
proper amount of additional oxygen is determined from the hydrogen
injection rate and the air inleakage rate and is controlled by the
hydrogen water chemistry (HWC) system.

SUMMARY

[0004] A method of controlling hydrogen concentrations in an offgas system
of a nuclear reactor by hydrogen water chemistry system injection may
include passively injecting ambient air through the hydrogen water
chemistry system into an existing offgas line of the offgas system. The
offgas line is configured to transport gases containing hydrogen, oxygen,
and other non-condensable gases from a condenser to a recombiner. The
recombiner is configured to react hydrogen with oxygen to form water
vapor.

[0005] A method of passively injecting air of a hydrogen water chemistry
system into an offgas system of a nuclear reactor according to a
non-limiting example embodiment of the present invention may include
operatively coupling an air injection line to an existing offgas line of
the offgas system. The offgas line is configured to transport offgas
containing hydrogen, oxygen, and other non-condensable gases from a
condenser to a recombiner. The air injection line is configured to
passively introduce ambient air into the offgas line at a point upstream
from the recombiner to produce a combined flow. The method also includes
measuring a concentration of at least one of hydrogen and oxygen in an
offgas flow exiting the recombiner. When used as a primary source of air,
the method additionally includes generating an injection signal whenever
the hydrogen water chemistry system is on. When used as a backup source
of oxygen, the method additionally includes generating an injection
signal as long as the measured oxygen concentration is lower than a
predetermined oxygen value or the measured hydrogen concentration exceeds
a predetermined hydrogen value. The method further includes automatically
opening a valve in response to the injection signal so as to passively
introduce ambient air as a source of oxygen into the offgas line. The
ambient air is drawn into the offgas line by a vacuum exerted by the
offgas system. The oxygen and hydrogen in the combined flow react in the
recombiner to form water vapor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The various features and advantages of the non-limiting embodiments
herein may become more apparent upon review of the detailed description
in conjunction with the accompanying drawings. The accompanying drawings
are merely provided for illustrative purposes and should not be
interpreted to limit the scope of the claims. The accompanying drawings
are not to be considered as drawn to scale unless explicitly noted. For
purposes of clarity, various dimensions of the drawings may have been
exaggerated.

[0007] FIG. 1 is a schematic of a hydrogen water chemistry system
utilizing passive air injection as a backup source of oxygen according to
an example embodiment of the invention.

[0008] FIG. 2 is a schematic of a hydrogen water chemistry system
utilizing passive air injection as a primary source of oxygen according
to an example embodiment of the invention.

[0009] FIG. 3 is a diagram of a passive air injection module according to
an example embodiment of the invention.

[0010]FIG. 4 is a layout of a passive air injection module according to
an example embodiment of the invention.

DETAILED DESCRIPTION

[0011] It should be understood that when an element or layer is referred
to as being "on," "connected to," "coupled to," or "covering" another
element or layer, it may be directly on, connected to, coupled to, or
covering the other element or layer or intervening elements or layers may
be present. In contrast, when an element is referred to as being
"directly on," "directly connected to," or "directly coupled to" another
element or layer, there are no intervening elements or layers present.
Like numbers refer to like elements throughout the specification. As used
herein, the term "and/or" includes any and all combinations of one or
more of the associated listed items.

[0012] It should be understood that, although the terms first, second,
third, etc. may be used herein to describe various elements, components,
regions, layers and/or sections, these elements, components, regions,
layers, and/or sections should not be limited by these terms. These terms
are only used to distinguish one element, component, region, layer, or
section from another region, layer, or section. Thus, a first element,
component, region, layer, or section discussed below could be termed a
second element, component, region, layer, or section without departing
from the teachings of example embodiments.

[0013] Spatially relative terms (e.g., "beneath," "below," "lower,"
"above," "upper," and the like) may be used herein for ease of
description to describe one element or feature's relationship to another
element(s) or feature(s) as illustrated in the figures. It should be
understood that the spatially relative terms are intended to encompass
different orientations of the device in use or operation in addition to
the orientation depicted in the figures. For example, if the device in
the figures is turned over, elements described as "below" or "beneath"
other elements or features would then be oriented "above" the other
elements or features. Thus, the term "below" may encompass both an
orientation of above and below. The device may be otherwise oriented
(rotated 90 degrees or at other orientations) and the spatially relative
descriptors used herein interpreted accordingly.

[0014] The terminology used herein is for the purpose of describing
various embodiments only and is not intended to be limiting of example
embodiments. As used herein, the singular forms "a," "an," and "the" are
intended to include the plural forms as well, unless the context clearly
indicates otherwise. It will be further understood that the terms
"comprises" and/or "comprising," when used in this specification, specify
the presence of stated features, integers, steps, operations, elements,
and/or components, but do not preclude the presence or addition of one or
more other features, integers, steps, operations, elements, components,
and/or groups thereof.

[0015] Example embodiments are described herein with reference to
cross-sectional illustrations that are schematic illustrations of
idealized embodiments (and intermediate structures) of example
embodiments. As such, variations from the shapes of the illustrations as
a result, for example, of manufacturing techniques and/or tolerances, are
to be expected. Example embodiments should not be construed as limited to
the shapes of regions illustrated herein but are to include deviations in
shapes that result, for example, from manufacturing. Thus, the regions
illustrated in the figures are schematic in nature and their shapes are
not intended to illustrate the actual shape of a region of a device and
are not intended to limit the scope of example embodiments.

[0016] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which example
embodiments belong. It will be further understood that terms; including
those defined in commonly used dictionaries, should be interpreted as
having a meaning that is consistent with their meaning in the context of
the relevant art and will not be interpreted in an idealized or overly
formal sense unless expressly so defined herein.

[0017] Example embodiments of the present invention relate to a method of
controlling hydrogen concentrations in an offgas system of a nuclear
reactor by hydrogen water chemistry system injection. The method may
include passively injecting ambient air through the hydrogen water
chemistry system into an existing offgas line of the offgas system. The
offgas line is configured to transport gases containing hydrogen, oxygen,
and other non-condensable gases from a condenser to a recombiner. The
recombiner is configured to react hydrogen with oxygen to form water
vapor.

[0018] The ambient air is passively injected into the offgas line at a
point upstream from the recombiner. The ambient air may be filtered prior
to injection into the offgas line. The ambient air may be passively
injected by opening an automatic valve and having the ambient air drawn
into the offgas line by a vacuum exerted by the offgas system. The
automatic valve may be an air-operated isolation valve that is controlled
through a solenoid valve. Alternatively, the automatic valve may be just
a solenoid valve. Furthermore, in a non-limiting embodiment, the vacuum
exerted by the offgas system may be generated by steam jet air ejectors
(SJAEs).

[0019] The ambient air may be passively injected at a desired flow into
the offgas line with a critical flow orifice. Alternatively, the ambient
air may be passively injected at a desired flow into the offgas line with
a flow meter and flow control valve. In a non-limiting embodiment, the
ambient air may be passively injected as a backup source of oxygen for
the hydrogen water chemistry system. In another non-limiting embodiment,
the ambient air may be passively injected as a primary source of oxygen
for the hydrogen water chemistry system.

[0020] A method of passively injecting air of a hydrogen water chemistry
system into an offgas system of a nuclear reactor according to a
non-limiting example embodiment of the present invention may include
operatively coupling an air injection line to an existing offgas line of
the offgas system. The offgas line is configured to transport offgas
containing hydrogen, oxygen, and other non-condensable gases from a
condenser to a recombiner. The air injection line is configured to
passively introduce ambient air into the offgas line at a point upstream
from the recombiner to produce a combined flow. The method also includes
measuring a concentration of at least one of hydrogen and oxygen in an
offgas flow exiting the recombiner. When used as a primary source of air,
the method additionally includes generating an injection signal whenever
the hydrogen water chemistry system is on. When used as a backup source
of oxygen, the method additionally includes generating an injection
signal as long as the measured oxygen concentration is lower than a
predetermined oxygen value or the measured hydrogen concentration exceeds
a predetermined hydrogen value. The method further includes automatically
opening a valve in response to the injection signal so as to passively
introduce ambient air as a source of oxygen into the offgas line. The
ambient air is drawn into the offgas line by a vacuum exerted by the
offgas system. The oxygen and hydrogen in the combined flow react in the
recombiner to form water vapor.

[0021] When used as a backup source of oxygen, the method may further
include generating a stop signal as long as the measured oxygen
concentration exceeds the predetermined oxygen value. The valve may be
automatically closed in response to the stop signal. The valve may be an
automatic isolation valve. In a non-limiting embodiment, the automatic
isolation valve may be an air-operated valve controlled through a
solenoid valve. Alternatively, the automatic isolation valve may be just
a solenoid valve. The ambient air may be filtered prior to introduction
into the offgas line. The ambient air may also contain about 21% oxygen.
The ambient air may be passively introduced into the offgas line at a
desired flow with a critical flow orifice. The critical flow orifice may
be sized based on ambient air and offgas pressures.

[0022] Controlling hydrogen concentrations in an offgas system of a
nuclear reactor according to example embodiments of the present invention
may involve the use of a passive air injection module. The passive air
injection module uses ambient air as an oxygen source for the hydrogen
water chemistry (HWC) system. As a result, the ambient air provides
oxygen to the offgas system to recombine with the hydrogen added to the
feedwater in the hydrogen water chemistry system. With appropriate sizing
of a valve trim and a critical flow orifice, the passive air injection
module is capable of providing the desired amount of constant air flow
into the offgas system. Thus, the passive air injection module can
function as a primary oxygen source or a backup oxygen source in a
hydrogen water chemistry system.

[0023] FIG. 1 is a schematic of a hydrogen water chemistry system
utilizing passive air injection as a backup source of oxygen according to
an example embodiment of the invention. Referring to FIG. 1, steam from
the reactor vessel 100 is supplied to the turbine/condenser 102, where
the steam is used to drive the turbine so as to generate electricity.
After passing through the turbine, the steam is condensed in the
condenser. The condensate is returned as feedwater to the reactor vessel
100, while the non-condensable gases are transported via an offgas line
to the recombiner 104.

[0024] A nuclear reactor typically experiences corrosion caused by oxygen
generated from the radiolysis of water. To reduce the amount of dissolved
oxygen within the recirculation piping, the reactor internals, and main
steam, a hydrogen injection unit 106 is used to inject hydrogen into the
condensate/feedwater. However, hydrogen injection into the
condensate/feedwater may result in hydrogen-rich offgas exiting the
recombiner 104. To prevent this potentially hazardous situation, an
oxygen injection unit 108 is used to inject oxygen into the offgas line.
Gas supplies 110 provide the hydrogen and oxygen to the hydrogen
injection unit 106 and oxygen injection unit 108, respectively.
Furthermore, a passive air injection module 114 is operatively coupled to
the offgas line via an air injection line. The passive air injection
module 114 may serve as a backup source of oxygen in the event that the
oxygen injection unit 108 or gas supply 110 fail or otherwise
malfunction.

[0025] The hydrogen concentration and/or oxygen concentration of the
offgas flow exiting the recombiner 104 is measured with a monitor 112. A
main control 116 is connected to the monitor 112 as well as the hydrogen
injection unit 106, the oxygen injection unit 108, the gas supply 110,
and the passive air injection module 114. At various times, the oxygen
concentration may fall below a predetermined oxygen value or the hydrogen
concentration may rise above a predetermined hydrogen value. Such changes
in the oxygen and/or hydrogen concentration may be caused by the
malfunction of one or more units (e.g., oxygen injection unit 108).
Accordingly, an injection signal is generated as long as the measured
oxygen concentration is lower than a predetermined oxygen value and/or
the measured hydrogen concentration exceeds a predetermined hydrogen
value or predetermined malfunctions occur. A valve of the passive air
injection module 114 may be automatically opened in response to the
injection signal so as to passively introduce ambient air as a source of
oxygen into the offgas line. The ambient air may be drawn into the offgas
line by a vacuum exerted by the offgas system so as to form a combined
flow with the non-condensable gases. The oxygen and hydrogen in the
combined flow react in the recombiner 104 to form water vapor

[0026] FIG. 2 is a schematic of a hydrogen water chemistry system
utilizing passive air injection as a primary source of oxygen according
to an example embodiment of the invention. The reactor vessel 200,
turbine/condenser 202, recombiner 204, hydrogen injection unit 206, gas
supply 210, monitor 212, passive air injection module 214, and main
control 216 of FIG. 2 correspond to the reactor vessel 100,
turbine/condenser 102, recombiner 104, hydrogen injection unit 106, gas
supply 110, monitor 112, passive air injection module 114, and main
control 116 of FIG. 1. Thus, the description of parts corresponding to
those already discussed will not be duplicated below for purposes of
brevity. FIG. 2 primarily differs from FIG. 1 in that the passive air
injection module 214 is utilized as a primary source of oxygen. Thus, a
unit corresponding to the oxygen injection unit 108 of FIG. 1 is absent
from FIG. 2. Because the passive air injection module 214 is being
utilized as a primary source of oxygen, the passive air injection module
214 may be configured to provide a constant, passive air flow into the
offgas line so as to control hydrogen concentrations in the offgas
system.

[0027] FIG. 3 is a diagram of a passive air injection module according to
an example embodiment of the invention. Referring to FIG. 3, the passive
air injection module 300 is configured to direct ambient air through
redundant valves to the injection line leading to the offgas system. The
injection point for the ambient air is upstream from the recombiner. The
passive air injection module 300 includes, for instance, one or more of
an air filter 301, automatic isolation valve (AOV) 302, valve position
switch 303, solenoid valve (SOV) 304, manual isolation valve 305,
pressure transmitter 306, critical flow orifice (CFO) 307, local pressure
gauge 308, piping, and control panel 310. The pressure transmitter 306
and valve position switches 303 send signals to the control panel 310.

[0028] One or more air filters 301 (e.g., 2--one for each redundant air
supply as shown in FIG. 4 as 401) filter the ambient air to meet plant
requirements for offgas cleanliness. The automatic isolation valve 302
opens when required for air injection into the offgas. The automatic
isolation valve 302 may be remotely-operated, air-to-close, and/or
spring-to-open. Valve position switches 303 may be mounted on each valve
assembly to indicate an open or closed valve position. Valve position may
be indicated at the control panel 310. The automatic isolation valve 302
may be automatically controlled through the solenoid valve 304 by
shutdown, reset, and start logic. Alternatively, the automatic isolation
valve 302 may be manually operated from the control panel 310.

[0029] A manual isolation valve 305 may be provided for the passive air
injection module 300 for isolation and maintenance. The pressure
transmitter 306 may provide a signal to the control panel 310 to indicate
air line pressure. The pressure transmitter 306 is normally exposed to
the condenser vacuum through the critical flow orifice 307. An increase
in pressure at the pressure transmitter 306 may indicate that at least
one automatic isolation valve 302 has opened and flow has actuated.

[0030] The critical flow orifice 307 may be sized based on ambient
pressure, inline components, and the offgas injection point pressure so
as to establish the desired air flow for air injection. A local pressure
gauge 308 may also alternatively function as a pressure indicator for air
flow information in the event the pressure transmitter 306 is inoperable.

[0031] Remote valve control switches in the control panel 310 may be used
to select a closed or permissive open (auto) setting for operation of the
automatic isolation valves 302. The closed position keeps the solenoid
valve 304 energized and the automatic isolation valve 302 closed. In the
auto position, the automatic isolation valve 302 will remain closed until
the logic sends a signal to open the automatic isolation valve 302. Where
the passive air injection module 300 includes a plurality of remote
valves 302 and their, control switches in the control panel 310, at least
one of the valve control switches must be in AUTO for the system to
start. For example, when the passive air injection module 300 is used as
a backup oxygen source, a warning alarm actuates if all valve control
switches are placed in CLOSE when the system is on. On the other hand,
when the passive air injection module 300 is used as the primary oxygen
source, the system will shut down if no automatic isolation valve 302 is
open.

[0032] As a backup oxygen source, the passive air injection module 300 is
intended to replace the oxygen injection should the oxygen injection unit
fail to properly inject oxygen during hydrogen injection. The passive air
flow from the module 300 is designed to prevent both a high offgas
hydrogen concentration and a high offgas oxygen concentration downstream
from the recombiner. Although various non-limiting situations are
discussed above, it should be understood that the passive air flow from
the module 300 may be designed to automatically actuate based on various
plant specific conditions.

[0034] According to the non-limiting example embodiments of the present
invention, controlling hydrogen concentrations in an offgas system of a
nuclear reactor by passive air injection results in fewer components and
maintenance requirements than if a conventional compressed air system or
compressed oxygen supply is chosen as an oxygen source. Because of the
fewer components and reduced maintenance, improved reliability and
availability may be achieved. Additionally, by using passive air
injection, the need for a unique/particular air supply system or oxygen
supply for a hydrogen water chemistry system (if used) is eliminated,
thereby avoiding unnecessary plant system interface. An air injection
module according to a non-limiting embodiment of the invention involves
little or no energy usage, since it is a passive system, by taking
advantage of the existing main condenser vacuum for motive force. The
passive air injection module may be utilized as a primary air supply or
as a backup air supply in the event an existing oxygen source becomes
inoperable.

[0035] While a number of example embodiments have been disclosed herein,
it should be understood that other variations may be possible. Such
variations are not to be regarded as a departure from the spirit and
scope of the present disclosure, and all such modifications as would be
obvious to one skilled in the art are intended to be included within the
scope of the following claims.